This invention relates generally to air brakes in railway cars and, more particularly, to Electrically Controlled Pneumatic Brakes (ECPBs) used with railcars.
For over one hundred years, train braking has been accomplished pneumatically. Pure air braking operates in the following manner. Air brakes on each car in a train respond to air signals from a brake pipe running the length of the train. When an engineer operates a locomotive brake valve to stop or slow the train, air pressure is reduced along the brake pipe, causing a brake control valve in each car to release air from a reservoir to apply the car brake. When brake pipe air pressure is increased, the brake control valve causes the brake to be released and allows the air supply reservoir to be recharged with air.
Because time is required for brake pipe air to travel from one car to the next, pure air braking is slow and uneven over the length of the train. For example, it can take as long as 15 seconds for a brake pipe pressure change to travel the length of a train having 150 cars. Accordingly, improvements have been made to air braking systems to quicken the braking process. One type of train braking equipment in common use, known as ABDW, is designed such that brake commands are sent as pressure pulses along the brake pipe, are acted upon by each car and sequentially accelerated to the next car. ABDW requirements are specified by the American Association of Railroads (AAR). (AAR also specifies requirements for ABDX equipment, which is similar to ABDW. Any reference herein to one of ABDW or ABDX is deemed to include the other equipment type.) A commonly used ABDW type of brake uses pressure-sensitive mechanical valves and pneumatic volumetric processing to control individual car brakes.
Electronic techniques are known which markedly improve air brake response time and functionality. For example, in Electrically Controlled Pneumatic (ECP) braking, electrical brake commands are sent from the locomotive to each car. Brake commands then are translated into electrical commands which electrically operate the brake control valve. Braking signal propagation time is reduced such that all cars are able to brake almost simultaneously.
Although ECP braking offers significant advantages over ABDW and other air braking systems, rapid conversion of all cars to ECP braking would be expensive. Thus electrical emulation of ABDW is known, whereby pneumatic brake commands are used, but brake air handling is performed electrically. For example, pressure-sensing transducers on a brake pipe detect pneumatic commands and send electrical signals to a computer, which uses the signals to control pneumatic brakes of each car.
ABDW emulation allows an ECP-ready car to operate as part of an ABDW-equipped train. ABDW emulation thus offers a flexible, incremental transition from ABDW-equipped trains to trains using only ECP. It is desirable to provide a simple, economical method for electrical emulation of ABDW in which the number of components is minimized. For even greater flexibility, it also is desirable to allow conventional ABDW cars to be included in trains equipped for ECP braking.
In one embodiment, a method for providing brake control for a rail car having a brake cylinder, a reservoir, and an exhaust vent includes the steps of fluidly interconnecting four electrically controlled valves between a train brake pipe, the brake cylinder, the reservoir, and the exhaust vent, and using an electronic brake controller to operate the valves to control air flow between the brake pipe, car brake cylinder, car reservoir, and exhaust vent. The method further includes configuring the electronic brake controller to respond to conventional pneumatic brake signals and to electronic brake signals, and configuring the electronic brake controller to control the valves to propagate pneumatic signals to other rail cars in a train in response to pneumatic and electronic brake signals.
The above-described valve assembly can withstand minor fluctuations in brake pipe pressure without applying an undesired emergency brake application. The above-described valve assembly operates in ECPB, mixed ECPB/ABDW, and pure ABDW modes of operation. Because the above described brake control system and method allow mixing of conventional ABDW rail cars with ECP-equipped cars in an ECP-equipped train, a gradual and cost-efficient changeover to pure ECP braking is facilitated.